Technologies that detect concealed objects are important to the National Security mission. Muons are naturally occurring subatomic particles that can be utilized to image concealed objects similarly to x-ray imaging but unobstructed by materials like lead. Muons can penetrate the earth's crust up to several kilometers. High-energy cosmic ray muons are more sensitive to density variation than other phenomena, including gravity. Their absorption rate depends on the density of the materials through which they pass. Measurements of muon flux rate at differing trajectories provide density variations of the materials between the muon source (cosmic rays and neutrino interactions) and detector, much like a CAT scan. Currently, muon tomography can resolve features to the sub-meter scale.
Additionally, muons are highly penetrating, traveling distances of several kilometers through the earth. Muons were used to image the interior of the Pyramid of Khafre of Giza in the 1960's. More recently, muons have been used to image volcanoes and smaller objects like contents of cargo containers. Muon technology is being developed to image a variety of objects including drugs, tunnels, and nuclear waste.
Presently, imaging subsurface objects like tunnels using muons can be costly and access prohibitive as muon sensors must be placed below objects being imaged. In addition, current muon detectors are limited in that the direction the muon is traveling is usually assumed to be from above (the direction of the vast majority of flux), rather than measured.
What is needed are muon detectors, systems and muon detection methods that can overcome the limitation of the prior art.